This invention relates to polyurethane foams. This invention particularly relates to polyurethane foams prepared from aqueous polyurethane dispersions, and to a process for preparing same.
Polyurethane dispersions are known and can be useful for preparing polyurethane polymers that can themselves be useful in various applications. Polyurethane dispersions can be used, for example, to prepare coatings for leather; wood finishing; glass fiber sizing; textiles; adhesives; and automotive topcoats and primers. Polyurethane dispersions can be prepared by various processes, including, for example, those described in: U.S. Pat. No. 4,857,565; U.S. Pat. No. 4,742,095; U.S. Pat. No. 4,879,322; U.S. Pat. No. 3,437,624; U.S. Pat. No. 5,037,864; U.S. Pat. No. 5,221,710; U.S. Pat. No. 4,237,264; and, U.S. Pat. No. 4,092,286.
It is known that carpet backings can be prepared from polyurethane dispersions. For example, polyurethane dispersions prepared according to the process of U.S. application Ser. No. 09/039,978, filed Mar. 16, 1998, now abandoned, can be useful for preparing polyurethane carpet backings and polyurethane textile backings. Typically, mechanical froths of dispersions which are applied as a primary or secondary binder to a carpet backing are unstable due to high concentration of filler and the absence of foam stabilizers. Mechanical frothing to produce a stable froth requires that less filler and foam stabilizers be used, and is therefore a distinctly different process than that conventionally used to coat the back of a carpet for primary or laminate applications. Mechanical frothing of currently commercially available polyurethane dispersions using air, for example, can be carried out using additives such as, for example, stabilizing soap, inorganic filler, and wax dispersions. While foams, on casting and drying, having good physical properties and stable fine cell structure up to 10 mm thickness can be prepared, the foams so prepared are not resilient.
Resiliency is a desirable characteristic for foams used in applications such as carpet backings. Increasing the resilience of such a foam can increase both the durability and comfort of the foams. For example, a more resilient foam, or stated another way, a "springy" foam is commonly perceived as more comfortable than a non-resilient foam. A more resilient foam can also dissipate energy mechanically, by springing back, rather than as heat such as would a non-resilient foam. Dissipating energy as heat can eventually cause polymer degradation which in turn leads to the foam not returning to its original shape. When this occurs in a carpet application, the resulting pattern evident on the surface of the carpet in normal traffic areas can be perceived as premature wear.
It would be desirable, in the art of preparing polyurethane foams, to have a polyurethane dispersion composition that can be mechanically frothed such that a foam having suitable fine cell structure and good properties, including resilience, can be prepared. It would also be desirable in the art to have a process for preparing a polyurethane foam having good resilience from a polyurethane dispersions by mechanically frothing the polyurethane dispersions.